Conventional optical zoom lenses function by moving sets of powered lens elements relative to each other along an optical axis. That is, the rotationally symmetric lens elements controllably move closer together and farther apart. This relative movement alters the focal length of the set of lens elements, producing a change in magnification of the set of lens elements and thence the zoom effect.
Another type of zoom lens, termed herein a “lateral shift zoom lens”, achieves the zooming effect by movement of multiple pairs of optical lens plates perpendicular to the optical axis. The lateral shift zoom lens, described in U.S. Pat. No. 4,925,281, utilizes rotationally nonsymmetric optical lens plates. The optical lens plates have shapes selected such that, when the pairs of optical lens plates are moved laterally relative to each other in a coordinated fashion, the focal length of the lens set changes. The shapes of the optical lens plates are selected such that the focal surface remains a focal plane, and so that the image remains in focus at the focal plane as the focal length and thence the magnification of the zoom lens changes. The lateral shift zoom lens has the advantage over conventional axial shift zoom lenses that the space required by the zoom lens does not lengthen as the zooming effect is achieved. The lateral shift zoom lens has limitations relative to conventional axial shift zoom lens in image quality, boresight pointing of the optical axis, and zooming range due to the asymmetric structure of the optical lens plates.
There is a need for an improved approach to lateral shift zoom lenses that would overcome at least some of the limitations of the current versions of the lateral shift zoom lens. The present invention fulfills this need, and further provides related advantages.
The present invention provides a zoom lens that achieves the zooming effect by translating lens plates perpendicular to, rather than parallel to, the optical axis. Additionally, the present approach provides control over the boresight pointing of the optical axis of the zoom lens. The optical axis may be held in a fixed direction or controllably pointed in a selected direction.
In accordance with the invention, an optical zoom lens mechanism arranged along an optical axis comprises a first lens group comprising at least two (and preferably exactly two) adjacent transparent first optical lens plates that are each rotationally nonsymmetric relative to the optical axis, and a first-group drive operable to move the first optical lens plates together and also by a first relative movement to each other in a first-movement radial direction relative to the optical axis. The optical zoom lens mechanism further includes a second lens group comprising at least two (and preferably exactly two) adjacent transparent second optical lens plates that are each rotationally nonsymmetric relative to the optical axis. The second lens group is spaced apart from the first lens group in an axial direction along the optical axis. A second-group drive is operable to move the second optical lens plates together and also by a second relative movement to each other in a second-movement radial direction relative to the optical axis. The first optical lens plates and the second optical lens plates are shaped so that the first relative movement of the first optical lens plates and the second relative movement of the second optical lens plates produces an optical zoom relative to a focal surface. There may be, and usually is, at least one additional lens lying on the optical axis.
The second-movement radial direction is angularly rotated from the first-movement radial direction by a nonzero rotational angle about the optical axis. The nonzero rotational angle is preferably at least 45 degrees. Most preferably, the nonzero rotational angle is about 90 degrees.
The first-group drive may be structured to produce a linear relative movement of the first optical lens plates. The first-group drive may instead be structured to produce a rotational relative movement of the first optical lens plates about a rotation axis parallel to but spaced apart from the optical axis. The second-group drive may also be a linear or rotational drive.
Each optical lens plate may be made of glass or other lens material that is transparent to visible light. The lens plates may instead be made of a material transparent to other wavelengths, such as silicon for infrared light.
To control the movement of the lens plates, there is preferably a microprocessor controller having a control output signal set operably connected to the first-group drive and to the second-group drive. In one embodiment, the microprocessor controller works from information developed during calibration procedures and stored in memory to select the positions to which the lens plates are driven to achieve any required combination of optical zooming and optical axis orientation. In another embodiment, the controller is a feedback controller comprising an imaging sensor, such as an imaging sensor located at the focal surface, and a microprocessor controller receiving an output of the imaging sensor and having a control output signal set operably connected to the first-group drive and to the second-group drive.
The lens plates in the two sets of lens groups are oriented and moved by their respective drives so that the relative movement has an orthogonal (perpendicular) component as between the two sets of lens groups. This orthogonal relative movement allows the pointing direction of the optical axis to be controllably set. The control of the direction of the optical axis may be used to keep the pointing direction fixed as the lens plates are moved to change the focal length of the zoom lens and thence achieve the zooming effect. The control of the direction of the optical axis may instead be used to aim the optical axis of the zoom lens in a selected direction.
This capability to both set the zooming conditions and control the direction of the optical axis greatly improves the potential utility of the lateral shift zoom lens. In the prior versions of the lateral shift zoom lens, the optical axis shifts uncontrollably as the lens plates are moved to effect the zoom action. This shifting of the optical axis is not a concern in some applications, but in others the precise position of features in the field of view relative to the boresight of the zoom lens must be known. The present approach achieves that result.
Other features and advantages of the present invention will be apparent from the following more detailed description of the preferred embodiment, taken in conjunction with the accompanying drawings, which illustrate, by way of example, the principles of the invention. The scope of the invention is not, however, limited to this preferred embodiment.